EMBRYONIC STEM CELL CORE CI B1. Establishment of the ES Cell Core: The ES Cell Core was founded with the support of this award and began operations -four years ago. It is located on the 9th Floor of the Wood Basic Science Building in -500 sq. ft. of space that is contiguous with the JHU SOM Transgenic Animal Facility. Dr. Woriey serves as the Director of the ES Cell Core and works closely with Dr. Roger Reeves, Director of the Transgenic Animal Facility, to integrate the functions of these Cores (see letter of support from Dr. Reeves (consultant)). Ms. Holly Wellington serves as Core Manager for this facility. The ES Cell Core reviews the design of targeting constructs, electroporates targeting construct DNA into ES cells, and then selects and amplifies ES cell colonies in duplicate 96 well plates;one plate is cryogenically stored and the other provided to investigators to screen for homologous recombination. The Core then grows promising ES cell clones, checks karyotypes and provides the targeted ES cells to the Transgenic Facility for injection into blastocysts.